The present invention relates to an arc stud welding device and method that applies electric power between a stud and a base material, generates a low current pilot arc between the stud and the base material, subsequently generates a high current main arc, and welds the stud to the base material.
In arc discharge welding, the arc stud welding device applies electric power between a stud and a base material, generates a low current pilot arc between the stud and the base material, subsequently generates a high current main arc, and welds the stud to the base material. This type of arc discharge welding is commonly known as drawn arc stud welding. One of these arc stud welding devices is disclosed in Japanese Unexamined Patent Application Publication [Kokai] No. 4-279280 (Patent Document 1: Japanese Patent No. 2,984,392).
The arc stud welding device disclosed in Japanese Unexamined Patent Application Publication [Kokai] No. 5-49172 (Patent Document 2) detects the current and voltage of the supplied electric power and controls the pilot arc current in order to generate an appropriate pilot arc. The arc stud welding device disclosed in Japanese Unexamined Patent Application Publication [Kokai] No. 2002-514972 (Patent Document 3: International Patent Application Publication No. WO96/11767) uses a reduced mass magnetic coil linear motor to move the stud holder at the tip of the welding gun.
In arc stud welding, power from the electric power source is applied to the base material and the stud brought into contact with the portion of the base material to be welded, the linear motor is operated to pull up the stud from the base material, a low current pilot arc is generated, the stud is pulled up farther while the pilot arc is being generated, a large current main arc is generated, the stud tip and the welded portion of the base material are melted, the linear motor is operated for a time allowing for sufficient melting, the stud is brought back into contact with the welded portion of the base material, and the stud is welded to the base material at a predetermined position.
In arc stud welding, the stud is brought into contact with the base material at the start of the welding operation. However, if the base material is flexible, and not rigid, the welded portion may become dented when the stud is brought into contact with it. As a result, the stud may sink below the level of the rest of the base material. When pulled up to generate the arc, the stud has to be raised to a predetermined height from the position where it made contact with the base material. However, if the base material was dented when the stud was brought into contact with it but returns to its original height when the stud is no longer bearing down on it, the stud pull up height is insufficient. If the pull up height is insufficient, the length of the generated arc is also insufficient and the resultant welding may be defective. If the sink-in depth due to stud contact is greater than the predetermined pull up height for the stud, the stud may not disengage when the base material returns to its original level. This makes arc generation impossible.